The present invention relates generally to magnetic torque-transferring devices and more particularly to those that employ a magnetically reactive medium for coupling together two relatively rotatable members.
Magnetic particle devices are known in the art. Generally, magnetic particle devices are based on electromagnetic and mechanical forces that act on a magnetically reactive medium disposed between the working surfaces of a driven member and driving member. The magnetic forces operate to increase the viscosity of the medium to interlock the driven and driving members. Magnetic particle devices are often designed as quick-acting electrically activated brakes or clutches for the transmission of torque. Alternatively, magnetic particle devices may be designed to impart drag between rotatable surfaces to maintain tension.
Where magnetic particle devices offer many advantages, such as low vibration torque transfer, the ability to operate in the slip condition, and the controllability of torque transfer over a relatively wide range of electrical input, there is a drawback as well. Conventional magnetic particle devices are relatively heavy due to the use of electromagnets as the source of a magnetic field. Known electromagnets generally comprise a shell with known magnetic properties and a coil of conductive wire. The thickness of the shell serves to define the working surface area of the device. Since the working surface is actually being coupled due to the increased viscosity of the magnetically reactive medium, an efficient design is one that maximizes the working surface area. Unfortunately, to increase working surface area in a conventional device, the thickness of the electromagnet shell must be increased, thereby undesirably increasing the weight.
Accordingly, there exists a need for a lightweight magnetic particle device that does not compromise working surface area or reduce operating life. The present invention provides an effective lightweight magnetic particle device wherein the reduction in weight is achieved without sacrificing working surface area or adversely affecting the operative life.
The present invention recognizes the disadvantages and limitations commonly associated with the operation of conventional magnetic particle devices. By constructing a magnetic particle device in accordance with an aspect of the current invention, the weight of the magnetic particle device can be significantly reduced without reducing working surface area or adversely affecting the operating life of the device.
In accordance with one embodiment of the present invention, a magnetic particle device is provided that includes a stationary housing, two relatively rotatable members, a rotatable shaft and a source of magnetic flux. The stationary housing is formed with a duct for receiving the rotatable shaft. The first rotatable member is mounted on the shaft and includes a cylindrical portion having a plurality of continuous annular grooves on the outer surface thereof. The second rotatable member is positioned radially outwardly of the first rotatable member defining a gap therebetween containing a magnetically reactive medium. The inner surface of the second rotatable member also includes a plurality of continuous annular grooves. A plurality of non-contacting annular sealing members impedes escape of the magnetically reactive particles from the gap.
The invention further includes an electromagnet comprising a rigid shell and a coil for generating a magnetic field defined by lines of magnetic flux in the vicinity of the electromagnet. The grooves in the first and second rotatable members cooperate to create a plurality of workings surfaces therebetween. The lines of magnetic flux travel a path substantially between the grooves through the working surfaces by traversing the gap so that the magnetically reactive particles lock into torque transmitting chains coupling the first rotatable member to the second. The use of multiple working surfaces allows the rigid shell surrounding the coil to be smaller in thickness and lighter in weight.
In accordance with a second embodiment of the present invention, a magnetic particle device is provided that is substantially similar to the first embodiment except that the plurality of grooves are located on the inner surface of the first rotatable member and the outer surface of the second rotatable member. This embodiment is advantageous because it imparts a significantly greater degree of drag between first and second rotatable members when the electromagnet is not energized.
In accordance with a third embodiment of the present invention, a magnetic particle device is provided that is substantially similar to the first embodiment except that the plurality of grooves are located both on the inner surface and outer surface of both the first and second rotatable members. The grooves are positioned such that said grooves radially oppose one another in each rotatable member. This embodiment is advantageous because it imposes a degree of drag greater than the first embodiment but less than the second embodiment when the electromagnet is not energized.
In accordance with a fourth embodiment of the present invention, a magnetic particle device is provided that is substantially similar to the first embodiment except that the first and second rotatable members include a plurality of apertures. The apertures in the first and second rotatable members cooperate to create a plurality of workings surfaces therebetween. The lines of magnetic flux travel a path substantially between the apertures through the working surfaces by traversing the gap so that the magnetically reactive particles lock into torque transmitting chains coupling the first rotatable member to the second. In addition to the advantages realized in the first embodiment, this embodiment is advantageous because it imparts no appreciable drag between the rotatable members in the absence of a magnetic field.
In accordance with a fifth embodiment of the present invention, a magnetic particle device is provided that is substantially similar to the first embodiment except that the first and second rotatable members comprise a plurality of alternating continuous magnetic and non-magnetic annular rings secured together by a plurality of fasteners. The continuous non-magnetic annular rings in the first and second rotatable members cooperate to create a plurality of workings surfaces therebetween. The magnetic flux travels a path substantially between the non-magnetic annular rings through the working surfaces by traversing the gap so that the magnetically reactive particles lock into torque transmitting chains coupling the first rotatable member to the second. In addition to the advantages realized in the first embodiment, this embodiment is advantageous because it may allow the device to impart a greater degree of drag between the rotatable members in the absence of magnetic flux.